Cruising RPM's

[Kim Schoedel]

The person I purchased our boat from told me that he always motored at 2000 RPM's and thus forward speed of 6 knots. Some where I read that the cruising speed for our boat is 7 knots. This would require much higher R's on the motor (22 hp Universal). I do have a work order for the local marina to check the engine alignment as there is some vibration created at certain speeds while motoring. This vibration is much more previlent when pushing over 2000 RPM's. Aside from the vibration thing, anyone out there have any thoughts on the cruising RPM's and forward speed? Thanks,

 

[Geoff Johnson]

I have the same engine and was cruising at about 2100 rpm which created a fair amount of black soot on the transom. My understanding is that the soot indicates the engine is working too hard. I had my Maxprop repitched and now cruise at about 2600 rpm. The soot has pretty much gone away.

 

[Loren Beach]

Hi Kim,
Could you give us the model of your engine.
In that era, the Universal M25 was installed quite a number of Ericsons, and it is rated at 21 hp.
In any case, it sounds like, at first blush, your boat is over-propped.
Loren

 

[Kim Schoedel]

RPM's

Thanks Geoff and Loren. Yes, I do have the older Maxprop 2 blade. I have not pushed the motor much over 2000 R's with the vibration thing. I am certain that the engine alignment is off since it come and goes at different levels of RPM's just like our old 30 catalina did before correcting the alignment. Yes, I believe it is the M25 3 cylinder, but don't have the data with me. To make things clear, I can go over 2000 R's but really don't want to until the alignment happens. Aside from this vibration thing, if every thing was wonderful, what do you think I should expect for cruising speed and at what RPM's? Thanks again

 

[Seth]

"Cruising speed"

Kim,

What do you mean by that term and where would you have read it? It is not a term that would normaly apply to a sailboat-under sail or power. Even the term "hull speed" is not very meaningful-since it is only a point at which an exponentially higher amount of power is needed to exceed, and which is fairly easy to attain with modest amounts of power. It basically explains why you might get to about 6 knots easily (1800-2000 rpms typically on most boats 32-40 feet), but might need 2700 or more RPM to get much above (assuming 6 knots is the hull speed). BTW-this is calculated as 1.34 X sq. root of LWL.

Having said all this, depending on installation, shaft aligment, and prop size and pitch, you will sometimes begin to get vibration like you describe at higher RPMs. If this occurs at a point beyond what you feel is a good speed, it is not a big problem. If it occurs below that, you should fix it. Most engines are fairly smooth up to at least 2500 RPMs. If they are high revving motors (VW, BMW, turbo Yanmars,etc.) you sould be able to get at least 3000 before much vibration..

Having said all that, for a moderate displacement 32 footer like yours with a 22 HP engine, 7 knots under power is pretty wishful thinking-certainly at "cruise power" settings (as defined in the ENGINE manual). Rarely do sailboats cruise that fast under power unless they are in the 42-58 foot range (because of the longer waterline). Frankly, for that boat 6 knots at 2K is pretty good.

Check the alignment, though!

Give us some more info about nwhere you you heard about 7 knots...
Good luck!,
S

 

[Kim Schoedel]

Thanks Seth, perhaps I am having a Senior moment!! Thought I read the 7 knot thing somewhere. Perhaps it was hull speed that I am thinking of. I am pleased with the 6 knots forward at 2000 R's. After the bottom is cleaned this spring I may get a few nano knots increase. More concerned about over reving the motor but it sounds like other folks are motoring at 2000 to 2500 R's.

 

[Seth]

No worries

You`are on the right track-and while I don't have the manual, any of these engines in that range can be run at 2500 or a bit more without problems-just buring a bit more fuel than at 2000, but should be fine...
Cheers,
S

 

[Loren Beach]

Strictly in the FWIW dept....
With a clean bottom we can do 6.9 to 7.0 at maximum usable RPM's, about 2900.
Following the guidelines in the Universal manual, I cruise at about 2500, give or take, and maintain over 6 kts.

Interestingly, our boat was quite over-propped when we bought it -- for the first year I thought it was supposed to motor at 1800 rpm...


Loren

 

[Kim Schoedel]

Thanks Loren! By the way, what is the FWIW dept? Is it the same dept as a "WAG". Please advise.

 

[Loren Beach]

acronyms R us...

For What It's Worth.... FWIW
By The Way.... BTW
On The Other Hand.... OTOH, what's a WAG?



Loren

(and the ever-useful: In My Humble Opinion... IMHO ! )

 

[Kim Schoedel]

BTW a WAG is "wild ass guess" and FWIW an EWAG is an "educated wild ass guess".

IMHO an EWAG is a contridiction of terms. How can a WAG be educated? A WAG is a WAG is a WAG.

 

[Geoff Johnson]

I have a 32-3 so this comment may not apply, but I have found that even with the smallest Maxprop I cannot get enough tip clearance which contributes to engine vibration (I think it's supposed to be 15% of the prop diameter). I even had the prop sent back to the factory to be ground smaller. I have had my engine realigned and still get some vibration at certain rpm's. Also, the 2 bladed Maxprop causes more vibration than the 3 bladed model. BTW, somewhere on the PYI web site is a formula that tells you how much to adjust the Maxprop to achieve a given increase in turning speed. It worked for me so that I didn't have to go through an expensive trial and error routine.

 

[Kim Schoedel]

Ok Geoff, I was wondering if the vibration was a by-product of the 2 blade Max. What I am getting is a slight vibration that comes on at certain rpm's then goes away if I decrease or increase engine speed. For instance, the vibes are basically non-exsistant at 2k but amplifly above 2k. Vibes come and go while passing through the 1300-1400 rpm range. I think I should still get the engine alignment checked and adjusted if need be. Just to be safe, don't want to have to pull the boat for a new cutlass bearing nor replace the nice stainless steel prop shaft that the previous owner put on a few years ago. Thanks again for your input.

 

[Chris Miller]

MUS method

Don't forget the MUS method... very helpful in doing taxes, job applications, etc... MUS=Make up S#^t
cm

 

[Geoff Johnson]

Kim, I have come to think is normal to have do things like stick a sponge under the sliding hatch to keep it from chattering when the engine is running. I think the boats respond to specific harmonics so you just have to find a speed that doesn't cause a shimmy. BTW, how do you know what your rpm's are? After I installed a TinyTach, I found my tachometer to be off by 200 rpms.

 

[Kim Schoedel]

FWIW a MUS normally preceeds a WAG. You need to MUS to do a WAG on your taxe's!!! And this works well for impressing land lubbers on their first sailing experience.

 

[Kim Schoedel]

Good point Geoff. The tach is the original. So far, just trusting that it is accurate is makeing me wonder. With the throttle as low as it goes (idle) the tach reads right at 1000 rpm's. I think the throttle cable adjustment is correct because the engine would labor and act weird I think if it were turning slower. Doe's 1000 r's seem high for an idle speed. I have no problem with any slaming when going into forward or reverse at an idle.

 

[NateHanson]

I agree, sounds like sympathetic vibrations. If they come and go, I'd be suprised if it were a shaft or alignment problem.

Try poking around below while the vibration is strong, and see if you can make it go away by sticking your foot here or there around the cabin and engineroom.

Nate

 

[John Wressell]

We have a Mark III 1983. 2000, 2100 RPM is about what I run at. You might want to check the cutlass bearing. Good idea to replace it from time to time,

John Wressell

 

[Geoff Johnson]

As I recall, my M25 idles at about 1200 rpms. BTW, if someone has installed a high output alternator, then your tach will be way off. For example, mine now reads 3000 when the engine is actually turning 2350. At $65, the TinyTach is a good investment and is, AFAIK, highly accurate since it works by reading the pulses in one of the high pressure fuel injector lines. It also keeps track of engine hours.

Accoring to the manual, the crusing range for this engine should be between 2100 and 2600 rpm's. I think the higher end of the range is better for the engine.

http://www.marinedieseldirect.com/universal/200157/universal-owners-manual-m25-specifications.html

However, it is a good idea to have someone check out the engine mounting. A couple of years ago I noticed some unusual vibrations and the yard discovered that the bolts for one of the motor mounts had worked loose. The holes had to be filled and redrilled.